The development of photofilm in small quantities by those, such as photo hobbyists or others, who require the capability of developing a few rolls of film at irregular intervals has led to the development of a number of the so-called daylight developing tanks. Essentially, the purpose of these devices is to permit film to be developed in small quantities without requiring the use of a full darkroom facility or a sequential developing machine, such as is common in the mass production of developed film.
All photofilm is light sensitive. Further, exposed photofilm, by reason of certain reactions that occur when the silver nitrate or other sensitized portion of the emulsion is exposed to light, is more sensitive to light than unexposed photofilm. Thus, there is a particular problem in handling exposed film which is to be developed in isolating it from any inadvertant light exposure while removing the film from the cartridge, in which it is encased, and placing it upon a mechanism which permits the free passage of chemicals so that the developing steps can freely progress.
The most widespread still picture film currently in commercial usage is provided, by a general industry standard, in the form of a 35mm-wide film having sprockets for mechanical movement of the film running each of two edges and is provided in certain fixed lengths upon small light-tight cassettes of a uniform construction. The majority of photo hobbyists use such film; in addition, a significant number of professional photographers also use this so-called 35 mm film.
The general steps to developing a single roll or a small number of rolls of such film start with the cassette of exposed film. It will be found that one end of the film protrudes from a light baffle opening on a side of the film cassette. This film end is then fastened to a reel having spacing system such as spiral ridges that permit film to be wound upon the reel, spacing sequential turns of the film a distance apart so as to permit the free passage of chemicals to facilitate development. The reel, so wound, is then immersed sequentially in a series of chemicals or rinses, all according to a particular pattern specified by the film manufacturer so as to permit the latent image on the film to be developed into a sensible, visual image.
It has become common to provide, for the chemical processing steps, a light-tight container which can hold the reels of film. Such containers usually comprise a closed container either of metal or of an opaque plastic, a removable light-tight baffled lid that permits the pouring in or pouring out of liquid solutions, and internal spaces or dimensions adapted to holding a finite number of reels of film. The reels are loaded in the dark with the film, inserted in the tank, and the light-tight lid placed upon the tank so as to enclose the reels. At this point the tank and lid protect the reel from exposure to light and the entire tank assembly can be manipulated in a lit area. For this reason these tanks have come to be known as daylight developing tanks.
A more limited number of developments have attempted to automate the loading of the reels for development process. Individual film cartridges for 35 mm must, for their intended use be light-tight; they contain a light baffle at the point where film exits or enters the cartridge. As a result, the reverse apparatus, daylight loaders for film cassettes from bulk reels of film, represent a relatively simpler problem and have long been available in the art. An apparatus for the loading of reels, however, must deal with the fact that film developing reels must be relatively open to permit the passage of chemicals and, for certain films, permit re-exposure to light, all as part of processing steps. As a result the film developing reels themselves cannot be light-tight. Thus, once film has been loaded upon developing reel, the entire reel must be permanently maintained in a dark condition, free from exposure to light. There are several kinds of loading reels among which two species are more popular, the so-called professional type which does not contain movable parts and is loaded by inserting one extreme of the film, or lead, on a retaining clip located near the center on the member that has attached to it both, top and bottom flanges. Once the film is secured and properly aligned, the operator presses both edges of the film to clear the outer grooves of reel as it is turned continuously to load it in an inside-out fashion pulling the film out of the casette.
The other type of reel has flanges that can be moved back and forth in a reciprocating manner. This type of reel is loaded by introducing a length of film in the take-up film grooves to a point where the film pulling or trapping elements are. Some models have a small steel ball and others have a protrusion that engages the film perforations. These two types trap the film edge when one of the flanges is moved clockwise, thus pulling the film out of the cassette. When said flange is returned (counterclockwise) it releases the grip on the film edge and the other flange traps the other film edge to prevent it from returning. These procedures are continued until entire film is loaded; since this operation is carried out by hand, there is the real risk of leaving finger marks or scratches. The perspiration on the fingers of the operator can damage the image area because it has a degree of acidity which acts as a fixer on the emulsion.
This requirement that the loaded developing reel be isolated from any light sources has lead to a restriction on most current daylight loading devices for developing reels that only one reel can be loaded and developed at a time. These devices are impractical when several rolls are to be developed. It obviously takes more time to develop one roll after another. But, furthermore the operator, after having developed a roll, must dry or wait until tank and reel are completely dry to procede with the development of the next roll, making the procedure a lengthier one. Alternatively, structures for the loading of multiple developing reels have required that the reels be gang-loaded; that is, the assemblage must be set up with all the necessary film cassettes and reels at one time and successful operation requires that the reels be loaded simultaneously by mechanical takeup means. Any jamming or defects not only endangers the specific film jammed, but also results in the destruction of all other rolls of film involved.
The fact that the reels must be exposed to chemicals also results in the necessity that the loading mechanism also is generally exposed to the chemical solutions. This not only produces severe adverse affects upon the loading mechanism, as many photo chemicals are intensively corrosive, but it also requires a relatively greater amount of chemistry per unit roll of film developed. Some of the existing one roll loading-developing tanks have the film cassette housing within the developing chamber, or connected to it by the film passage corridor without a provision to hermetically separate one from the other. So when the chemicals are poured in for processing they also flood or fill the cassette housing and film passage corridor making it necessary to utilize extra amounts of chemicals to reach a level to properly bathe the entire film. The tank shown in U.S. Pat. No. 2,434,033 (German) has a film cassette holding chamber within the developing chamber thus increasing the inner dimensions and making it necessary to use a larger amount of chemicals. Photo chemicals are expensive, and also pose some degree of environmental hazard, and creating disposal problems, such wastage of photo chemicals is to be avoided. Other tanks have the loading means or peripheral projection for receiving the cassette, in such a disposition that, during the agitation of the developer, this projection will cause a disturbance creating an uneven flow that can result in an uneven development. U.S. Pat. No. 3,703,859 shows a tank to load a "plurality of rolls" adapted for 16 MM. If this tank were to be also adapted for 35 MM film, it would be necessary to increase the diameter of the tank to a very large and impractical size to accommodate the length of these films. It would require more chemicals per roll and it would only work with films having the same length since it could not properly unwind films of different lengths. Its construction would only allow movement to unwind the shortest roll.
U.S. Pat. No. 2,082,962 shows a single roll loading and developing tank that contains a reel in a vertical position; the inventor indicates that little amount of chemicals is necessary for processing since the reel is in this vertical position, the tank needs to be only half-full, thus covering half of the reel, which therefore has to be revolved continuously to develop the film. It is to be noted here that such continuous agitation during development results in a highly "contrasty" negative. It is known that when the developer is touching the film emulsion the developing power of the developer is diminished in the portions of the image that have been more exposed to light. This fact permits the less exposed areas to be developed at a relatively faster rate rendering a more balanced image. Manufacturers of film indicate that the developing film should be stirred once ever so often. This replenishes the developer in the high density areas at the opportune intervals.
The continuous stirring of the developing roll therefore renders a high contrast unbalanced and uncontrolled developed image.